The present disclosure relates to a hollow product configured as an insert-molded product, including an insert-molded tubular member, and a method of making the hollow product. More particularly, the present disclosure relates to a hollow product in which the tubular member and a material surrounding the tubular member have been partially removed, and a method of making such a product.
Recently, to achieve a low fuel cost, a downsized turbocharger is more and more often built in automobile engines. A turbocharger attached to an engine of this type includes an impeller and a compressor housing to house the impeller. The compressor housing generally has a scroll shape with an undercut portion (see, for example, Japanese Unexamined Patent Publications No. 2016-160941, No. 2016-84710, and No. 2012-57592, and Japanese Translation of PCT International Application Publication No. 2016-536501).
In the turbochargers disclosed in Japanese Unexamined Patent Publications No. 2016-160941, No. 2016-84710, and No. 2012-57592, and Japanese Translation of PCT International Application Publication No. 2016-536501, their compressor housing has, at its central portion, an impeller housing portion to house the impeller. On the outer periphery of the compressor housing, an air passage is provided to extend around the impeller housing portion. A circumferential portion of a circumferential wall that defines the air passage is locally opened to make the air passage communicate with the impeller housing portion. The air, flowing out of the impeller housing portion, flows into the air passage through the opened portion of the air passage, and then flows out of the air passage through a downstream end thereof to be fed to the engine.
In general, the air passage of the compressor housing has a nearly circular or elliptical cross section and usually has a so-called “undercut shape” which prevents a die from passing through it. The compressor housing is just an example of various hollow products with such an undercut shape. There are many other products of that type.
If a hollow product with such an undercut shape is made of an aluminum alloy, for example, the hollow product may be formed by a sand mold casting process which uses a core that is removable by a process step after the casting process. Alternatively, when the hollow product is formed by die-casting, a plurality of parts may be once produced separately and then assembled together.
The sand mold casting process using a core results in poor productivity because the process takes a cycle time of as long as about five minutes. Meanwhile, according to the die-casting process, the respective parts need to be formed separately and then assembled together, thus raising the manufacturing cost, which is not beneficial.
In view of the foregoing background, it is therefore an object of the present disclosure to cut down the cost of making a hollow product by allowing the product to be molded integrally in a shorter cycle time.